Extending multichip package link off package

ABSTRACT

An interconnect interface is provided to enable communication with an off-package device over a link including a plurality of lanes. Logic of the interconnect interface includes receiver logic to receive a valid signal from the off-package device on a dedicated valid lane of the link indicating that data is to arrive on a plurality of dedicated data lanes in the plurality of lanes, receive the data on the data lanes from the off-package device sampled based on arrival of the valid signal, and receive a stream signal from the off-package device on a dedicated stream lane in the plurality of lanes. The stream signal corresponds to the data and indicates a particular data type of the data. The particular data type can be one of a plurality of different data types capable of being received on the plurality of data lanes of the link.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 U.S.C. § 120) of U.S. patent application Ser. No. 17/860,587,filed Jul. 8, 2022, which is a continuation of U.S. patent applicationSer. No. 17/121,534, filed Dec. 14, 2020, and entitled “ExtendingMultichip Package Link Off Package”, which is a continuation of U.S.patent application Ser. No. 16/946,109, filed Jun. 5, 2020, now U.S.Pat. No. 11,113,225, issued Sep. 7, 2021, and entitled “ExtendingMultichip Package Link Off Package”, which is a continuation of U.S.patent application Ser. No. 15/761,401, filed Mar. 19, 2018, now U.S.Pat. No. 10,678,736, issued Jun. 9, 2020, and entitled “ExtendingMultichip Package Link Off Package”, which is a national stageapplication under 35 U.S.C. § 371 of PCT International ApplicationSerial No. PCT/US2015/052160, filed on Sep. 25, 2015, and entitled“Extending Multichip Package Link Off Package”. The disclosures of theprior applications are considered part of and are hereby incorporated byreference in their entirety in the disclosure of this application.

FIELD

This disclosure pertains to computing system, and in particular (but notexclusively) to point-to-point interconnects.

BACKGROUND

Advances in semi-conductor processing and logic design have permitted anincrease in the amount of logic that may be present on integratedcircuit devices. As a corollary, computer system configurations haveevolved from a single or multiple integrated circuits in a system tomultiple cores, multiple hardware threads, and multiple logicalprocessors present on individual integrated circuits, as well as otherinterfaces integrated within such processors. A processor or integratedcircuit typically comprises a single physical processor die, where theprocessor die may include any number of cores, hardware threads, logicalprocessors, interfaces, memory, controller hubs, etc.

As a result of the greater ability to fit more processing power insmaller packages, smaller computing devices have increased inpopularity. Smartphones, tablets, ultrathin notebooks, and other userequipment have grown exponentially. However, these smaller devices arereliant on servers both for data storage and complex processing thatexceeds the form factor. Consequently, the demand in thehigh-performance computing market (i.e. server space) has alsoincreased. For instance, in modern servers, there is typically not onlya single processor with multiple cores, but also multiple physicalprocessors (also referred to as multiple sockets) to increase thecomputing power. But as the processing power grows along with the numberof devices in a computing system, the communication between sockets andother devices becomes more critical.

In fact, interconnects have grown from more traditional multi-drop busesthat primarily handled electrical communications to full blowninterconnect architectures that facilitate fast communication.Unfortunately, as the demand for future processors to consume at evenhigher-rates corresponding demand is placed on the capabilities ofexisting interconnect architectures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a computing system including aninterconnect architecture.

FIG. 2 illustrates an embodiment of a interconnect architectureincluding a layered stack.

FIG. 3 illustrates an embodiment of a request or packet to be generatedor received within an interconnect architecture.

FIG. 4 illustrates an embodiment of a transmitter and receiver pair foran interconnect architecture.

FIG. 5A illustrates an embodiment of a multichip package.

FIG. 5B illustrates an embodiment of a multichip package interconnectedwith at least one off-package device.

FIG. 6 is a simplified block diagram of a multichip package link (MCPL).

FIG. 7 is a representation of example signaling on an example MCPL.

FIG. 8 is a simplified block diagram illustrating a data lane in anexample MCPL.

FIG. 9 is a simplified block diagram illustrating example crosstalkcancellation techniques in an embodiment of an MCPL.

FIG. 10 is a simplified circuit diagram illustrating example crosstalkcancellation components in an embodiment of an MCPL.

FIG. 11 is a simplified block diagram of an MCPL.

FIG. 12 is a simplified block diagram of an MCPL interfacing with upperlayer logic of multiple protocols using a logical PHY interface (LPIF).

FIG. 13 is a representation of example signaling on an example MCPL inconnection with a recovery of a link.

FIGS. 14A-14C are example bit mappings of data on lanes of an exampleMCPL.

FIG. 15 is a representation of a portion of an example link statemachine.

FIG. 16 is a representation of a flow associated with an examplecentering of a link.

FIG. 17 is a representation of an example link state machine.

FIG. 18 is a representation of signaling to enter a low power state.

FIG. 19 is a block diagram illustrating example compliance testing ofMCPL transmitter logic.

FIG. 20 is a block diagram illustrating example compliance testing ofMCPL receiver logic.

FIG. 21 is a block diagram illustrating interconnection of two switchesusing an example MCPL.

FIG. 22 is a block diagram of a portion of a circuit board utilizing anexample MCPL.

FIGS. 23A-23B are block diagrams illustrating partitioning of exampleMCPL logic.

FIG. 24 illustrates an embodiment of a block for a computing systemincluding multiple processors.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth,such as examples of specific types of processors and systemconfigurations, specific hardware structures, specific architectural andmicro architectural details, specific register configurations, specificinstruction types, specific system components, specificmeasurements/heights, specific processor pipeline stages and operationetc. in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art thatthese specific details need not be employed to practice the presentinvention. In other instances, well known components or methods, such asspecific and alternative processor architectures, specific logiccircuits/code for described algorithms, specific firmware code, specificinterconnect operation, specific logic configurations, specificmanufacturing techniques and materials, specific compilerimplementations, specific expression of algorithms in code, specificpower down and gating techniques/logic and other specific operationaldetails of computer system haven't been described in detail in order toavoid unnecessarily obscuring the present invention.

Although the following embodiments may be described with reference toenergy conservation and energy efficiency in specific integratedcircuits, such as in computing platforms or microprocessors, otherembodiments are applicable to other types of integrated circuits andlogic devices. Similar techniques and teachings of embodiments describedherein may be applied to other types of circuits or semiconductordevices that may also benefit from better energy efficiency and energyconservation. For example, the disclosed embodiments are not limited todesktop computer systems or Ultrabooks™. And may be also used in otherdevices, such as handheld devices, tablets, other thin notebooks,systems on a chip (SOC) devices, and embedded applications. Someexamples of handheld devices include cellular phones, Internet protocoldevices, digital cameras, personal digital assistants (PDAs), andhandheld PCs. Embedded applications typically include a microcontroller,a digital signal processor (DSP), a system on a chip, network computers(NetPC), set-top boxes, network hubs, wide area network (WAN) switches,or any other system that can perform the functions and operations taughtbelow. Moreover, the apparatus', methods, and systems described hereinare not limited to physical computing devices, but may also relate tosoftware optimizations for energy conservation and efficiency. As willbecome readily apparent in the description below, the embodiments ofmethods, apparatus', and systems described herein (whether in referenceto hardware, firmware, software, or a combination thereof) are vital toa ‘green technology’ future balanced with performance considerations.

As computing systems are advancing, the components therein are becomingmore complex. As a result, the interconnect architecture to couple andcommunicate between the components is also increasing in complexity toensure bandwidth requirements are met for optimal component operation.Furthermore, different market segments demand different aspects ofinterconnect architectures to suit the market's needs. For example,servers require higher performance, while the mobile ecosystem issometimes able to sacrifice overall performance for power savings. Yet,it's a singular purpose of most fabrics to provide highest possibleperformance with maximum power saving. Below, a number of interconnectsare discussed, which would potentially benefit from aspects of theinvention described herein.

One interconnect fabric architecture includes the Peripheral ComponentInterconnect (PCI) Express (PCIe) architecture. A primary goal of PCIeis to enable components and devices from different vendors tointer-operate in an open architecture, spanning multiple marketsegments; Clients (Desktops and Mobile), Servers (Standard andEnterprise), and Embedded and Communication devices. PCI Express is ahigh performance, general purpose I/O interconnect defined for a widevariety of future computing and communication platforms. Some PCIattributes, such as its usage model, load-store architecture, andsoftware interfaces, have been maintained through its revisions, whereasprevious parallel bus implementations have been replaced by a highlyscalable, fully serial interface. The more recent versions of PCIExpress take advantage of advances in point-to-point interconnects,Switch-based technology, and packetized protocol to deliver new levelsof performance and features. Power Management, Quality Of Service (QoS),Hot-Plug/Hot-Swap support, Data Integrity, and Error Handling are amongsome of the advanced features supported by PCI Express.

Referring to FIG. 1 , an embodiment of a fabric composed ofpoint-to-point Links that interconnect a set of components isillustrated. System 100 includes processor 105 and system memory 110coupled to controller hub 115. Processor 105 includes any processingelement, such as a microprocessor, a host processor, an embeddedprocessor, a co-processor, or other processor. Processor 105 is coupledto controller hub 115 through front-side bus (FSB) 106. In oneembodiment, FSB 106 is a serial point-to-point interconnect as describedbelow. In another embodiment, link 106 includes a serial, differentialinterconnect architecture that is compliant with different interconnectstandard.

System memory 110 includes any memory device, such as random accessmemory (RAM), non-volatile (NV) memory, or other memory accessible bydevices in system 100. System memory 110 is coupled to controller hub115 through memory interface 116. Examples of a memory interface includea double-data rate (DDR) memory interface, a dual-channel DDR memoryinterface, and a dynamic RAM (DRAM) memory interface.

In one embodiment, controller hub 115 is a root hub, root complex, orroot controller in a Peripheral Component Interconnect Express (PCIe orPCIE) interconnection hierarchy. Examples of controller hub 115 includea chipset, a memory controller hub (MCH), a northbridge, an interconnectcontroller hub (ICH), a southbridge, and a root controller/hub. Oftenthe term chipset refers to two physically separate controller hubs, i.e.a memory controller hub (MCH) coupled to an interconnect controller hub(ICH). Note that current systems often include the MCH integrated withprocessor 105, while controller 115 is to communicate with I/O devices,in a similar manner as described below. In some embodiments,peer-to-peer routing is optionally supported through root complex 115.

Here, controller hub 115 is coupled to switch/bridge 120 through seriallink 119. Input/output modules 117 and 121, which may also be referredto as interfaces/ports 117 and 121, include/implement a layered protocolstack to provide communication between controller hub 115 and switch120. In one embodiment, multiple devices are capable of being coupled toswitch 120.

Switch/bridge 120 routes packets/messages from device 125 upstream, i.e.up a hierarchy towards a root complex, to controller hub 115 anddownstream, i.e. down a hierarchy away from a root controller, fromprocessor 105 or system memory 110 to device 125. Switch 120, in oneembodiment, is referred to as a logical assembly of multiple virtualPCI-to-PCI bridge devices. Device 125 includes any internal or externaldevice or component to be coupled to an electronic system, such as anI/O device, a Network Interface Controller (NIC), an add-in card, anaudio processor, a network processor, a hard-drive, a storage device, aCD/DVD ROM, a monitor, a printer, a mouse, a keyboard, a router, aportable storage device, a Firewire device, a Universal Serial Bus (USB)device, a scanner, and other input/output devices. Often in the PCIevernacular, such as device, is referred to as an endpoint. Although notspecifically shown, device 125 may include a PCIe to PCI/PCI-X bridge tosupport legacy or other version PCI devices. Endpoint devices in PCIeare often classified as legacy, PCIe, or root complex integratedendpoints.

Graphics accelerator 130 is also coupled to controller hub 115 throughserial link 132. In one embodiment, graphics accelerator 130 is coupledto an MCH, which is coupled to an ICH. Switch 120, and accordingly I/Odevice 125, is then coupled to the ICH. I/O modules 131 and 118 are alsoto implement a layered protocol stack to communicate between graphicsaccelerator 130 and controller hub 115. Similar to the MCH discussionabove, a graphics controller or the graphics accelerator 130 itself maybe integrated in processor 105.

Turning to FIG. 2 an embodiment of a layered protocol stack isillustrated. Layered protocol stack 200 includes any form of a layeredcommunication stack, such as a Quick Path Interconnect (QPI) stack, aPCie stack, a next generation high performance computing interconnectstack, or other layered stack. Although the discussion immediately belowin reference to FIGS. 1-4 are in relation to a PCIe stack, the sameconcepts may be applied to other interconnect stacks. In one embodiment,protocol stack 200 is a PCIe protocol stack including transaction layer205, link layer 210, and physical layer 220. An interface, such asinterfaces 117, 118, 121, 122, 126, and 131 in FIG. 1 , may berepresented as communication protocol stack 200. Representation as acommunication protocol stack may also be referred to as a module orinterface implementing/including a protocol stack.

PCI Express uses packets to communicate information between components.Packets are formed in the Transaction Layer 205 and Data Link Layer 210to carry the information from the transmitting component to thereceiving component. As the transmitted packets flow through the otherlayers, they are extended with additional information necessary tohandle packets at those layers. At the receiving side the reverseprocess occurs and packets get transformed from their Physical Layer 220representation to the Data Link Layer 210 representation and finally(for Transaction Layer Packets) to the form that can be processed by theTransaction Layer 205 of the receiving device.

Transaction Layer

In one embodiment, transaction layer 205 is to provide an interfacebetween a device's processing core and the interconnect architecture,such as data link layer 210 and physical layer 220. In this regard, aprimary responsibility of the transaction layer 205 is the assembly anddisassembly of packets (i.e., transaction layer packets, or TLPs). Thetranslation layer 205 typically manages credit-base flow control forTLPs. PCIe implements split transactions, i.e. transactions with requestand response separated by time, allowing a link to carry other trafficwhile the target device gathers data for the response.

In addition PCIe utilizes credit-based flow control. In this scheme, adevice advertises an initial amount of credit for each of the receivebuffers in Transaction Layer 205. An external device at the opposite endof the link, such as controller hub 115 in FIG. 1 , counts the number ofcredits consumed by each TLP. A transaction may be transmitted if thetransaction does not exceed a credit limit. Upon receiving a response anamount of credit is restored. An advantage of a credit scheme is thatthe latency of credit return does not affect performance, provided thatthe credit limit is not encountered.

In one embodiment, four transaction address spaces include aconfiguration address space, a memory address space, an input/outputaddress space, and a message address space. Memory space transactionsinclude one or more of read requests and write requests to transfer datato/from a memory-mapped location. In one embodiment, memory spacetransactions are capable of using two different address formats, e.g., ashort address format, such as a 32-bit address, or a long addressformat, such as 64-bit address. Configuration space transactions areused to access configuration space of the PCIe devices. Transactions tothe configuration space include read requests and write requests.Message space transactions (or, simply messages) are defined to supportin-band communication between PCIe agents.

Therefore, in one embodiment, transaction layer 205 assembles packetheader/payload 206. Format for current packet headers/payloads may befound in the PCIe specification at the PCIe specification website.

Quickly referring to FIG. 3 , an embodiment of a PCIe transactiondescriptor is illustrated. In one embodiment, transaction descriptor 300is a mechanism for carrying transaction information. In this regard,transaction descriptor 300 supports identification of transactions in asystem. Other potential uses include tracking modifications of defaulttransaction ordering and association of transaction with channels.

Transaction descriptor 300 includes global identifier field 302,attributes field 304 and channel identifier field 306. In theillustrated example, global identifier field 302 is depicted comprisinglocal transaction identifier field 308 and source identifier field 310.In one embodiment, global transaction identifier 302 is unique for alloutstanding requests.

According to one implementation, local transaction identifier field 308is a field generated by a requesting agent, and it is unique for alloutstanding requests that require a completion for that requestingagent. Furthermore, in this example, source identifier 310 uniquelyidentifies the requestor agent within a PCIe hierarchy. Accordingly,together with source ID 310, local transaction identifier 308 fieldprovides global identification of a transaction within a hierarchydomain.

Attributes field 304 specifies characteristics and relationships of thetransaction. In this regard, attributes field 304 is potentially used toprovide additional information that allows modification of the defaulthandling of transactions. In one embodiment, attributes field 304includes priority field 312, reserved field 314, ordering field 316, andno-snoop field 318. Here, priority sub-field 312 may be modified by aninitiator to assign a priority to the transaction. Reserved attributefield 314 is left reserved for future, or vendor-defined usage. Possibleusage models using priority or security attributes may be implementedusing the reserved attribute field.

In this example, ordering attribute field 316 is used to supply optionalinformation conveying the type of ordering that may modify defaultordering rules. According to one example implementation, an orderingattribute of “0” denotes default ordering rules are to apply, wherein anordering attribute of “1” denotes relaxed ordering, wherein writes canpass writes in the same direction, and read completions can pass writesin the same direction. Snoop attribute field 318 is utilized todetermine if transactions are snooped. As shown, channel ID Field 306identifies a channel that a transaction is associated with.

Link Layer

Link layer 210, also referred to as data link layer 210, acts as anintermediate stage between transaction layer 205 and the physical layer220. In one embodiment, a responsibility of the data link layer 210 isproviding a reliable mechanism for exchanging Transaction Layer Packets(TLPs) between two components a link. One side of the Data Link Layer210 accepts TLPs assembled by the Transaction Layer 205, applies packetsequence identifier 211, i.e. an identification number or packet number,calculates and applies an error detection code, i.e. CRC 212, andsubmits the modified TLPs to the Physical Layer 220 for transmissionacross a physical to an external device.

Physical Layer

In one embodiment, physical layer 220 includes logical sub block 221 andelectrical sub-block 222 to physically transmit a packet to an externaldevice. Here, logical sub-block 221 is responsible for the “digital”functions of Physical Layer 221. In this regard, the logical sub-blockincludes a transmit section to prepare outgoing information fortransmission by physical sub-block 222, and a receiver section toidentify and prepare received information before passing it to the LinkLayer 210.

Physical block 222 includes a transmitter and a receiver. Thetransmitter is supplied by logical sub-block 221 with symbols, which thetransmitter serializes and transmits onto to an external device. Thereceiver is supplied with serialized symbols from an external device andtransforms the received signals into a bit-stream. The bit-stream isde-serialized and supplied to logical sub-block 221. In one embodiment,an 8b/10b transmission code is employed, where ten-bit symbols aretransmitted/received. Here, special symbols are used to frame a packetwith frames 223. In addition, in one example, the receiver also providesa symbol clock recovered from the incoming serial stream.

As stated above, although transaction layer 205, link layer 210, andphysical layer 220 are discussed in reference to a specific embodimentof a PCIe protocol stack, a layered protocol stack is not so limited. Infact, any layered protocol may be included/implemented. As an example,an port/interface that is represented as a layered protocol includes:(1) a first layer to assemble packets, i.e. a transaction layer; asecond layer to sequence packets, i.e. a link layer; and a third layerto transmit the packets, i.e. a physical layer. As a specific example, acommon standard interface (CSI) layered protocol is utilized.

Referring next to FIG. 4 , an embodiment of a PCIe serial point to pointfabric is illustrated. Although an embodiment of a PCIe serialpoint-to-point link is illustrated, a serial point-to-point link is notso limited, as it includes any transmission path for transmitting serialdata. In the embodiment shown, a basic PCIe link includes two,low-voltage, differentially driven signal pairs: a transmit pair 406/411and a receive pair 412/407. Accordingly, device 405 includestransmission logic 406 to transmit data to device 410 and receivinglogic 407 to receive data from device 410. In other words, twotransmitting paths, i.e. paths 416 and 417, and two receiving paths,i.e. paths 418 and 419, are included in a PCIe link.

A transmission path refers to any path for transmitting data, such as atransmission line, a copper line, an optical line, a wirelesscommunication channel, an infrared communication link, or othercommunication path. A connection between two devices, such as device 405and device 410, is referred to as a link, such as link 415. A link maysupport one lane — each lane representing a set of differential signalpairs (one pair for transmission, one pair for reception). To scalebandwidth, a link may aggregate multiple lanes denoted by xN, where N isany supported Link width, such as 1, 2, 4, 8, 12, 16, 32, 64, or wider.

A differential pair refers to two transmission paths, such as lines 416and 417, to transmit differential signals. As an example, when line 416toggles from a low voltage level to a high voltage level, i.e. a risingedge, line 417 drives from a high logic level to a low logic level, i.e.a falling edge. Differential signals potentially demonstrate betterelectrical characteristics, such as better signal integrity, i.e.cross-coupling, voltage overshoot/undershoot, ringing, etc. This allowsfor better timing window, which enables faster transmission frequencies.

FIG. 5A is a simplified block diagram 500 a illustrating an examplemulti-chip package 505 that includes two or more chips, or dies, (e.g.,510, 515) communicatively connected using an example multi-chip packagelink (MCPL) 520. While FIG. 5 illustrates an example of two (or more)dies that are interconnected using an example MCPL 520, it should beappreciated that the principles and features described herein regardingimplementations of an MCPL can be applied to any interconnect or linkconnecting a die (e.g., 510) and other components, including connectingtwo or more dies (e.g., 510, 515), connecting a die (or chip) to anothercomponent off-die, connecting a die to another device or dieoff-package, connecting die to a BGA package, implementation of a Patchon Interposer (POINT), among potentially other examples. For instance,FIG. 5B, illustrates an implementation where an MCPL can be extendedfrom an on-package interconnection (as shown in FIG. 5A) to includelinks connecting two devices not included on the same package.

Continuing with the example of FIG. 5A, generally, a multichip package(e.g., 505) can be an electronic package where multiple integratedcircuits (ICs), semiconductor dies or other discrete components (e.g.,510, 515) are packaged onto a unifying substrate (e.g., silicon or othersemiconductor substrate), facilitating the combined components' use as asingle component (e.g., as though a larger IC). In some instances, thelarger components (e.g., dies 510, 515) can themselves be IC systems,such as systems on chip (SoC), multiprocessor chips, or other componentsthat include multiple components (e.g., 525-530 and 540-545) on thedevice, for instance, on a single die (e.g., 510, 515). Multichippackages 505 can provide flexibility for building complex and variedsystems from potentially multiple discrete components and systems. Forinstance, each of dies 510, 515 may be manufactured or otherwiseprovided by two different entities, with the silicon substrate of thepackage 505 provided by yet a third entity, among many other examples.Further, dies and other components within a multichip package 505 canthemselves include interconnect or other communication fabrics (e.g.,535, 550) providing the infrastructure for communication betweencomponents (e.g., 525-530 and 540-545) within the device (e.g., 510, 515respectively). The various components and interconnects (e.g., 535, 550)may potentially support or use multiple different protocols. Further,communication between dies (e.g., 510, 515) can potentially includetransactions between the various components on the dies over multipledifferent protocols. Designing mechanisms to provide communicationbetween chips (or dies) on a multichip package can be challenging, withtraditional solutions employing highly specialized, expensive, andpackage-specific solutions based on the specific combinations ofcomponents (and desired transactions) sought to be interconnected.

The examples, systems, algorithms, apparatus, logic, and featuresdescribed within this Specification can address at least some of theissues identified above, including potentially many others notexplicitly mentioned herein. For instance, in some implementations, ahigh bandwidth, low power, low latency interface can be provided toconnect a host device (e.g., a CPU) or other device to a companion chipthat sits in the same package as the host. Such a multichip package link(MCPL) can support multiple package options, multiple I/O protocols, aswell as Reliability, Availability, and Serviceability (RAS) features.Further, the physical layer (PHY) can include an electrical layer andlogic layer and can support longer channel lengths, including channellengths up to, and in some cases exceeding, approximately 45 mm. In someimplementations, an example MCPL can operate at high data rates,including data rates exceeding 8-10 Gb/s.

In one example implementation of an MCPL, a PHY electrical layer canimprove upon traditional multi-channel interconnect solutions (e.g.,multi-channel DRAM I/O), extending the data rate and channelconfiguration, for instance, by a number of features including, asexamples, regulated mid-rail termination, low power active crosstalkcancellation, circuit redundancy, per bit duty cycle correction anddeskew, line coding, and transmitter equalization, among potentiallyother examples.

In one example implementation of an MCPL, a PHY logical layer can beimplemented that can further assist (e.g., electrical layer features) inextending the data rate and channel configuration while also enablingthe interconnect to route multiple protocols across the electricallayer. Such implementations can provide and define a modular commonphysical layer that is protocol agnostic and architected to work withpotentially any existing or future interconnect protocol.

Turning to the simplified block diagram 500 b shown in FIG. 5B,multi-protocol, time-multiplexed MCPLs (e.g., 520 a) can be utilized tonot only interconnect two or more components, or devices, (e.g., 510,515) on the same package (e.g., 505), but the (hardware and/or software)logic used to implement MCPLs can also be utilized to connect devicesnot located on the same package. Such links can be physically longerthan those interconnecting components in close proximity within a singlepackage. As one example, a package device 505 can interconnect with oneor more other devices (e.g., 560, 565) provided on a board 570 with thepackage device 505. One or more interfaces 575 can be provided on thepackage to acts as a slot through which the functionality and componentsof the package 505 can be extended to incorporate additional off-packagecomponents (e.g., 560, 565). The interface can include logic identicalto, or similar to, that utilized in the on-package components supportingMCPLs (e.g., 520 a). According, corresponding MCPLs (e.g., 520 b, 520 c)can be provided to connect the interface(s) 575 with off-packagecomponents 565, 570 and support multi-protocol, time-multiplexed databetween the package 505 and the components 565, 570. In someimplementations, the interface(s) 575 can be further interconnected withon-package components (e.g., 510, 515) using similar instances of MCPLs(e.g., 520 d), among other example implementations and architectures.

Turning to FIG. 6 , a simplified block diagram 600 is shown representingat least a portion of a system including an example implementation of amultichip package link (MCPL). An MCPL can be implemented using physicalelectrical connections (e.g., wires implemented as lanes) connecting afirst device 605 (e.g., a first die including one or moresub-components) with a second device 610 (e.g., a second die includingone or more other sub-components). In the particular example shown inthe high-level representation of diagram 600, all signals (in channels615, 620) can be unidirectional and lanes can be provided for the datasignals to have both an upstream and downstream data transfer. While theblock diagram 600 of FIG. 6 , refers to the first component 605 as theupstream component and the second component 610 as the downstreamcomponents, and physical lanes of the MCPL used in sending data as adownstream channel 615 and lanes used for receiving data (from component610) as an upstream channel 620, it should be appreciated that the MCPLbetween devices 605, 610 can be used by each device to both send andreceive data between the devices.

In one example implementation, an MCPL can provide a physical layer(PHY) including the electrical MCPL PHY 625 a,b (or, collectively, 625)and executable logic implementing MCPL logical PHY 630 a,b (or,collectively, 630). Electrical, or physical, PHY 625 can provide thephysical connection over which data is communicated between devices 605,610. Signal conditioning components and logic can be implemented inconnection with the physical PHY 625 in order to establish high datarate and channel configuration capabilities of the link. For on-packageMCPLs, tightly clustered physical connections can provided at lengths ofapproximately 45 mm or more. Longer lengths (i.e., multiple times longerthan on-package connections (e.g., greater than 200 mm)) can be providedfor off-package connections. The logical PHY 630 can include logic forfacilitating clocking, link state management (e.g., for link layers 635a, 635 b), and protocol multiplexing between potentially multiple,different protocols used for communications over the MCPL.

In one example implementation, physical PHY 625 can include, for eachchannel (e.g., 615, 620) a set of data lanes, over which in-band datacan be sent. In this particular example, 50 data lanes are provided ineach of the upstream and downstream channels 615, 620, although anyother number of lanes can be used as permitted by the layout and powerconstraints, desired applications, device constraints, etc. Each channelcan further include one or more dedicated lanes for a strobe, or clock,signal for the channel, one or more dedicated lanes for a valid signalfor the channel, one or more dedicated lanes for a stream signal, andone or more dedicated lanes for a link state machine management orsideband signal. The physical PHY can further include a sideband link640, which, in some examples, can be a bi-directional lower frequencycontrol signal link used to coordinate state transitions and otherattributes of the MCPL connecting devices 605, 610, among otherexamples.

In some implementations, data lanes can be provided as clusters, such asclusters of 4, 8, 16, 20, or 24 lanes. Multiple clusters can be assignedto implement particular portions of the MCPL (e.g., upstream ordownstream data lanes, etc.). In cases where the number of data lanes isnot a multiple of the size of clusters utilized to implement the datalanes (e.g., multiple clusters of 20 lanes combined to implement an MCPLof 50 lanes), remaining unused lanes (e.g., 10 extra lanes) can bededicated to facilitate dynamic replacement of marginal lanes, allowingdata of a marginal lane to be re-routed using the free “extra” lanes ina cluster. In some implementations, such as on-package MCPLs withsmaller lengths, data sampling of data lanes can be completed on aper-cluster basis (e.g., all lanes in a cluster are trained together asa unitary whole) rather than training or synchronizing each lane in thecluster on a per-lane basis (as may be desirable when the MCPL connectstwo devices (not on-package) over longer distances, among other examplesand uses.

As noted above, multiple protocols can be supported using animplementation of MCPL. Indeed, multiple, independent transaction layers650 a, 650 b can be provided at each device 605, 610. For instance, eachdevice 605, 610 may support and utilize two or more protocols, such asPCI, PCIe, QPI, Intel In-Die Interconnect (IDI), among others. IDI is acoherent protocol used on-die to communicate between cores, Last LevelCaches (LLCs), memory, graphics, and 10 controllers. Other protocols canalso be supported including Ethernet protocol, Infiniband protocols, andother PCIe fabric based protocols. The combination of the Logical PHYand physical PHY can also be used as a die-to-die interconnect toconnect a serializer/deserializer (SerDes) PHY (PCIe, Ethernet,Infiniband or other high speed SerDes) on one Die to its upper layersthat are implemented on the other die, among other examples.

Logical PHY 630 can support multiplexing between these multipleprotocols on an MCPL. Data of different protocols can be multiplexed todefined windows of time (or unit intervals of data), allowing thesedifferent types of data to be time-multiplexed on the same link. In oneexample, the dedicated stream lane can be used to assert an encodedstream signal that identifies which protocol is to apply to data sentsubstantially concurrently on the data lanes of the channel. Further,logical PHY 630 can be used to negotiate the various types of link statetransitions that the various protocols may support or request. In someinstances, LSM_SB signals sent over the channel's dedicated LSM_SB lanecan be used, together with side band link 640 to communicate andnegotiate link state transitions between the devices 605, 610. Further,link training, error detection, skew detection, de-skewing, and otherfunctionality of traditional interconnects can be replaced or governed,in part using logical PHY 630. For instance, valid signals sent over oneor more dedicated valid signal lanes in each channel can be used tosignal link activity, detect skew, link errors, and realize otherfeatures, among other examples. In the particular example of FIG. 6 ,multiple valid lanes are provided per channel. For instance, data laneswithin a channel can be bundled or clustered (physically and/orlogically) and a valid lane can be provided for each cluster. Further,multiple strobe lanes can be provided, in some cases, also to provide adedicated strobe signal for each cluster in a plurality of data laneclusters in a channel, among other examples.

As noted above, logical PHY 630 can be used to negotiate and manage linkcontrol signals sent between devices connected by the MCPL. In someimplementations, logical PHY 630 can include link layer packet (LLP)generation logic 660 that can be used to send link layer controlmessages over the MCPL (i.e., in band). Such messages can be sent overdata lanes of the channel, with the stream lane identifying that thedata is link layer-to-link layer messaging, such as link layer controldata, among other examples. Link layer messages enabled using LLP module660 can assist in the negotiation and performance of link layer statetransitioning, power management, loopback, disable, re-centering,scrambling, among other link layer features between the link layers 635a, 635 b of devices 605, 610 respectively.

Turning to FIG. 7 , a diagram 700 is shown representing examplesignaling using a set of lanes (e.g., 615, 620) in a particular channelof an example MCPL. In the example of FIG. 7 , two clusters oftwenty-five (25) data lanes are provided for fifty (50) total data lanesin the channel. A portion of the lanes are shown, while others (e.g.,DATA[4-46] and a second strobe signal lane (STRB)) are omitted (e.g., asredundant signals) for convenience in illustrating the particularexample. When the physical layer is in an active state (e.g., notpowered off or in a low power mode (e.g., an L1 state)), strobe lanes(STRB) can be provided with a synchronous clock signal. In someimplementations, data can be sent on both the rising and falling edgesof the strobe. Each edge (or half clock cycle) can demarcate a unitinterval (UI), realizing a 2UI clock. Accordingly, in this example, abit (e.g., 705) can be sent on each lane, allowing for a byte to be sentevery 8UI (or every 4 clock (STRB) cycles). A byte time period 710 canbe defined as 8UI, or the time for sending a byte on a single one of thedata lanes (e.g., DATA[0-49]). In one example, the byte time period 710can be defined as a signaling window in which a chunk of data of any oneof a plurality of different types can be sent. Subsequent chunks, orstreams, of data can be sent in subsequent, defined windows.

In some implementations, a valid signal, sent on one or more dedicatedvalid signal channels (e.g., VALID0, VALID1), can serve as a leadingindicator for the receiving device (or “sink”) to identify, whenasserted (high), that data is being sent from the sending device (or“source”) on data lanes (e.g., DATA[0-49]) during the immediatelyfollowing data signaling window, such as a byte time period 710.Alternatively, when the valid signal is low, the source indicates to thesink that the sink will not be sending data on the data lanes during thefollowing time period. Accordingly, when the sink logical PHY detectsthat the valid signal is not asserted (e.g., on lanes VALID0 andVALID1), the sink can disregard any data that is detected on the datalanes (e.g., DATA[0-49]) during the following time period. For instance,crosstalk noise or other transient bits may appear on one or more of thedata lanes when the source, in fact, is not sending any data. By virtueof a low, or non-asserted, valid signal during the previous time period(e.g., the previous byte time period), the sink can determine thatactivity the data lanes are to be disregarded during the following timeperiod, or signaling window.

Data sent on each of the lanes of the MCPL can be strictly aligned tothe strobe signal. A time period can be defined based on the strobe,such as a byte time period, and each of these periods can correspond toa defined window in which signals are to be sent on the data lanes(e.g., DATA[0-49]), the valid lanes (e.g., VALID1, VALID2), and streamlane (e.g., STREAM). Accordingly, alignment of these signals can enableidentification that a valid signal in a previous time period windowapplies to data in the following time period window, and that a streamsignal applies to data in the same time period window. The stream signalcan be an encoded signal (e.g., 1 byte of data for a byte time periodwindow), that is encoded to identify the protocol that applies to databeing sent during the same time period window. Training of an MCPL canensure that sampling of the valid lanes and corresponding data lanes (aswell as the corresponding stream lanes) are strictly aligned, given thedependence of receiving logic on the accurate timing of correspondingvalid signals on the valid lanes.

As an illustrative example, as shown in FIG. 7 , a byte time periodsignaling window is defined and data is prepared to be sent in thewindow. A valid is asserted at a time period window n (715), before anydata is injected on data lanes DATA[0-49] during the identified window.At the following time period window n+1 (720) data is sent on at leastsome of the data lanes. In this case, data is sent on all fifty datalanes during n+1 (720). Because a valid was asserted for the duration ofthe preceding time period window n (715), the sink device can validatethe data received on data lanes DATA[0-49] during time period window n+1(720). Additionally, the leading nature of the valid signal during timeperiod window n (715) allows the receiving device to prepare for andaccurately sample the incoming data. Continuing with the example of FIG.7 , the valid signal remains asserted (on VALID1 and VALID2) during theduration of time period window n+1 (720), causing the sink device toexpect the additional data (of the same or a different type) to be sentover data lanes DATA[0-49] during the immediately succeeding time periodwindow n+2 (725). If the valid signal were to remain asserted duringtime period window n+2 (725), the sink device could further expect toreceive (and process) additional data sent during an immediatelysubsequent time period window n+3 (730). In the example of FIG. 7 ,however, the valid signal is de-asserted following the conclusion oftime period window n+1 (720) and remains low during the duration of timeperiod window n+2 (725), indicating to the sink device that no data willbe sent during time period window n+3 (730) and that any bits detectedon data lanes DATA[0-49] should be disregarded during time period windown+3 (730).

As noted above, multiple valid lanes and strobe lanes can be maintainedper channel. This can assist, among other advantages, with maintainingcircuit simplicity and synchronization amid the clusters of relativelylengthy physical lanes connecting the two devices. In someimplementations, a set of data lanes can be divided into clusters ofdata lanes. For instance, in the example of FIG. 7 , data lanesDATA[0-49] can be divided into two twenty-five lane clusters and eachcluster can have a dedicated valid and strobe lane. For instance, validlane VALID1 can be associated with data lanes DATA[0-24] and valid laneVALID2 can be associated with data lanes DATA[25-49]. The signals oneach “copy” of the valid and strobe lanes for each cluster can beidentical.

As introduced above, data on stream lane STREAM can be used to indicateto the receiving logical PHY what protocol is to apply to correspondingdata being sent on data lanes data lanes DATA[0-49]. In the example ofFIG. 7 , a stream signal is sent on STREAM during the same time periodwindow as data on data lanes DATA[0-49] to indicate the protocol of thedata on these data lanes. In alternative implementations, the streamsignal can be sent during a preceding time period window, such as withcorresponding valid signals, among other potential modifications.However, continuing with the example of FIG. 7 , a stream signal 735 issent during time period window n+1 (720) that is encoded to indicate theprotocol (e.g., PCIe, PCI, IDI, QPI, etc.) that is to apply to the bitssent over data lanes DATA[0-49] during the same time period window n+1(720). Similarly, another stream signal 740 can be sent during thesubsequent time period window n+2 (725) to indicate the protocol thatapplies to the bits sent over data lanes DATA[0-49] during time periodwindow n+2 (725), and so on. In some cases, such as the example of FIG.7 (where both stream signals 735, 740 have the same encoding, binaryFF), data in sequential time period windows (e.g., n+1 (720) and n+2(725)) can belong to the same protocol. However, in other cases, data insequential time period windows (e.g., n+1 (720) and n+2 (725)) can befrom different transactions to which different protocols are to apply,and stream signals (e.g., 735, 740) can be encoded accordingly toidentify the different protocols applying to the sequential bytes ofdata on the data lanes (e.g., DATA[0-49]) (such as shown in the exampleof FIG. 7 ), among other examples.

In some implementations, a low power or idle state can be defined forthe MCPL. For instance, when neither device on the MCPL is sending data,the physical layer (electrical and logical) of MCPL can go to an idle orlow power state. For instance, in the example of FIG. 7 , at time periodwindow n−2 (745), the MCPL is in a quiet or idle state and the strobe isdisabled to save power. The MCPL can transition out of low-power or idlemode, awaking the strobe at time period window time period window n−1(e.g., 705). The strobe can complete a transmission preamble (e.g., toassist in waking and synchronizing each of the lanes of the channel, aswell as the sink device), beginning the strobe signal prior to any othersignaling on the other non-strobe lanes. Following this time periodwindow n−1 (705), the valid signal can be asserted at time period windown (715) to notify the sink that data is forthcoming in the followingtime period window n+1 (720), as discussed above.

The MCPL may re-enter a low power or idle state (e.g., an L1 state)following the detection of idle conditions on the valid lanes, datalanes, and/or other lanes of the MCPL channel. For instance, nosignaling may be detected beginning at time period window n+3 (730) andgoing forward. Logic on either the source or sink device can initiatetransition back into a low power state leading again (e.g., time periodwindow n+5 (755)) to the strobe going idle in a power savings mode,among other examples and principles (including those discussed laterherein).

Electrical characteristics of the physical PHY can include one or moreof single-ended signaling, half-rate forwarded clocking, matching ofinterconnect channel as well as on-chip transport delay of transmitter(source) and receiver (sink), optimized electrostatic discharge (ESD)protection, pad capacitance, among other features. Further, an MCPL canbe implemented to achieve higher data rate (e.g., approaching 16 Gb/s)and energy efficiency characteristics than traditional package I/Osolutions.

FIG. 8 illustrates a portion of a simplified block diagram 800representing a portion of an example MCPL. The diagram 800 of FIG. 8includes a representation of an example lane 805 (e.g., a data lane,valid lane, or stream lane) and clock generation logic 810. As shown inthe example of FIG. 8 , in some implementations, clock generation logic810 can be implemented as a clock tree to distribute the generated clocksignal to each block implementing each lane of the example MCPL, such asdata lane 805. Further, a clock recovery circuit 815 can be provided. Insome implementations, rather than providing a separate clock recoverycircuit for each lane in which the clock signal is distributed, as iscustomary in at least some traditional interconnect I/O architectures, asingle clock recovery circuit can be provided for a cluster of aplurality of lanes. Indeed, as applied to the example configurations inFIGS. 6 and 7 , a separate strobe lane and accompanying clock recoverycircuit can be provided for each cluster of twenty-five data lanes.

Continuing with the example of FIG. 8 , in some implementations, atleast the data lanes, stream lanes, and valid lanes can be terminated,mid-rail, to a regulated voltage greater than zero (ground). In someimplementations, a mid-rail voltage can be regulated to Vcc/2. In someimplementations, a single voltage regulator 825 can be provided percluster of lanes. For instance, when applied to the examples of FIGS. 6and 7 , a first voltage regulator can be provided for a first cluster oftwenty-five data lanes and a second voltage regulator can be providedfor the remaining cluster of twenty-five data lanes, among otherpotential examples. In some instances, an example voltage regulator 825can be implemented as a linear regulator, a switched capacitor circuit,among other examples. In some implementations, the linear regulator canbe provided with analog feedback loop or digital feedback loop, amongother examples.

In some implementations, crosstalk cancellation circuitry can also beprovided for an example MCPL. In some instances, the compact nature ofthe long MCPL wires can introduce crosstalk interference between lanes.Crosstalk cancellation logic can be implemented to address these andother issues. For instance, in one example illustrated in FIGS. 9-10 ,crosstalk can be reduced significantly with an example low power activecircuit, such as illustrated in diagrams 900 and 1000. For instance, inthe example of FIG. 9 , a weighted high-pass filtered “aggressor” signalcan be added to the “victim” signal (i.e., the signal sufferingcrosstalk interference from the aggressor). Each signal can beconsidered a victim of crosstalk from each other signal in the link, andcan, itself, be the aggressor to the other signal insofar it is thesource of crosstalk interference. Such a signal can be generated andreduce crosstalk on the victim lane by more than 50%, owing to thederivative nature of crosstalk on the link. The low pass filteredaggressor signal, in the example of FIG. 9 , can be generated through ahigh-pass RC filter (e.g., implemented through C and R1) that producesthe filtered signal to be added using a summing circuit 905 (e.g., RXsense-amp).

Implementations similar to that described in the example of FIG. 9 canbe particularly convenient solutions for an application such as MCLP, asimplementation of the circuit can be realized with relatively lowoverhead, as illustrated in the diagram of FIG. 10 illustrating anexample transistor-level schematic of the circuit shown and described inthe example of FIG. 9 . It should be appreciated that therepresentations in FIGS. 9 and 10 are simplified representations, and anactual implementation would include multiple copies of the circuitsillustrated in FIGS. 9 and 10 to accommodate the network of crosstalkinterference among and between the lanes of a link. As an example, in athree lane link (e.g., Lanes 0-2) circuitry similar to that described inthe examples of FIGS. 9 and 10 could be provided from Lane 0 to Lane 1,from Lane 0 to Lane 2, from Lane 1 to Lane 0, from Lane 1 to Lane 2,from Lane 2 to Lane 0, from Lane 2 to Lane 1, etc. based on the geometryand the layout of the lanes, among other examples

Additional features can be implemented at the physical PHY level of anexample MCPL. For instance, receiver offset can introduce significanterror and limit I/O voltage margin in some instances. Circuit redundancycan be used to improve receiver sensitivity. In some implementations,circuit redundancy can be optimized to address the standard deviationoffset of data samplers used in the MCPL. For instance, an example datasampler can be provided that is designed to a three (3) standarddeviation offset specification. In the examples of FIGS. 6 and 7 , forinstance, were two (2) data samplers to be used for each receiver (e.g.,for each lane), one hundred (100) samplers would be used for a fifty(50) lane MCPL. In this example, the probability that one of thereceiver (RX) lanes fails the three standard deviation offsetspecification is 24%. A chip reference voltage generator can be providedto set the offset upper-bound and move to the next data sampler on thereceiver if another one of the other data samplers is found to beexceeding the bound. However, were four (4) data samplers to be used perreceiver (i.e., instead of two in this example), the receiver will onlyfail if three out of four samplers fail. For a fifty-lane MCPL, as inthe examples of FIGS. 6 and 7 , adding this additional circuitredundancy can dramatically reduce the failure rate from 24% to lessthan 0.01%.

In still other examples, at very high data rates, per bit duty cyclecorrection (DCC) and deskew can be used to augment baseline per clusterDCC and deskew to improve link margin. Instead of correction for allcases, as in traditional solutions, in some implementations a low powerdigital implementation can be utilized that senses and corrects theoutliers where the I/O lane would fail. For instance, a global tuning ofthe lanes can be performed to identify problem lanes within the cluster.These problem lanes can then be targeted for per-lane tuning to achievethe high data rates supported by the MCPL.

Additional features can also be optionally implemented in some examplesof a MCPL to enhance the performance characteristics of the physicallink. For instance, line coding can be provided. While mid-railterminations, such as described above, can allow for DC data businversion (DBI) to be omitted, AC DBI can still be used to reduce thedynamic power. More complicated coding can also be used to eliminate theworst case difference of 1's and 0's to reduce, for instance, the driverequirement of mid-rail regulator, as well as limit I/O switching noise,among other example benefits. Further, transmitter equalization can alsobe optionally implemented. For instance, at very high data rates,insertion loss can be a significant for an in-package channel. A two-tapweight transmitter equalization (e.g., performed during an initialpower-up sequence) can, in some cases, be sufficient to mitigate some ofthese issues, among others.

Turning to FIG. 11 , a simplified block diagram 1100 is shownillustrating an example logical PHY of an example MCPL. A physical PHY1105 can connect to a die that includes logical PHY 1110 and additionallogic supporting a link layer of the MCPL. The die, in this example, canfurther include logic to support multiple different protocols on theMCPL. For instance, in the example of FIG. 11 , PCIe logic 1115 can beprovided as well as IDI logic 1120, such that the dies can communicateusing either PCIe or IDI over the same MCPL connecting the two dies,among potentially many other examples, including examples where morethan two protocols or protocols other than PCIe and IDI are supportedover the MCPL. Various protocols supported between the dies can offervarying levels of service and features.

Logical PHY 1110 can include link state machine management logic 1125for negotiating link state transitions in connection with requests ofupper layer logic of the die (e.g., received over PCIe or IDI). LogicalPHY 1110 can further include link testing and debug logic (e.g., 1130)ion some implementations. As noted above, an example MCPL can supportcontrol signals that are sent between dies over the MCPL to facilitateprotocol agnostic, high performance, and power efficiency features(among other example features) of the MCPL. For instance, logical PHY1110 can support the generation and sending, as well as the receivingand processing of valid signals, stream signals, and LSM sidebandsignals in connection with the sending and receiving of data overdedicated data lanes, such as described in examples above.

In some implementations, multiplexing (e.g., 1135) and demultiplexing(e.g., 1140) logic can be included in, or be otherwise accessible to,logical PHY 1110. For instance, multiplexing logic (e.g., 1135) can beused to identify data (e.g., embodied as packets, messages, etc.) thatis to be sent out onto the MCPL. The multiplexing logic 1135 canidentify the protocol governing the data and generate a stream signalthat is encoded to identify the protocol. For instance, in one exampleimplementation, the stream signal can be encoded as a byte of twohexadecimal symbols (e.g., IDI: FFh; PCIe: F0h; LLP: AAh; sideband: 55h;etc.), and can be sent during the same window (e.g., a byte time periodwindow) of the data governed by the identified protocol. Similarly,demultiplexing logic 1140 can be employed to interpret incoming streamsignals to decode the stream signal and identify the protocol that is toapply to data concurrently received with the stream signal on the datalanes. The demultiplexing logic 1140 can then apply (or ensure)protocol-specific link layer handling and cause the data to be handledby the corresponding protocol logic (e.g., PCIe logic 1115 or IDI logic1120).

Logical PHY 1110 can further include link layer packet logic 1150 thatcan be used to handle various link control functions, including powermanagement tasks, loopback, disable, re-centering, scrambling, etc. LLPlogic 1150 can facilitate link layer-to-link layer messages over MCLP,among other functions. Data corresponding to the LLP signaling can bealso be identified by a stream signal sent on a dedicated stream signallane that is encoded to identify that the data lanes LLP data.Multiplexing and demultiplexing logic (e.g., 1135, 1140) can also beused to generate and interpret the stream signals corresponding to LLPtraffic, as well as cause such traffic to be handled by the appropriatedie logic (e.g., LLP logic 1150). Likewise, as some implementations ofan MCLP can include a dedicated sideband (e.g., sideband 1155 andsupporting logic), such as an asynchronous and/or lower frequencysideband channel, among other examples.

Logical PHY logic 1110 can further include link state machine managementlogic that can generate and receive (and use) link state managementmessaging over a dedicated LSM sideband lane. For instance, an LSMsideband lane can be used to perform handshaking to advance linktraining state, exit out of power management states (e.g., an L1 state),among other potential examples. The LSM sideband signal can be anasynchronous signal, in that it is not aligned with the data, valid, andstream signals of the link, but instead corresponds to signaling statetransitions and align the link state machine between the two die orchips connected by the link, among other examples. Providing a dedicatedLSM sideband lane can, in some examples, allow for traditional squelchand received detect circuits of an analog front end (AFE) to beeliminated, among other example benefits.

Turning to FIG. 12 , a simplified block diagram 1200 is shownillustrating another representation of logic used to implement an MCPL.For instance, logical PHY 1110 is provided with a defined logical PHYinterface (LPIF) 1205 through which any one of a plurality of differentprotocols (e.g., PCIe, IDI, QPI, etc.) 1210, 1215, 1220, 1225 andsignaling modes (e.g., sideband) can interface with the physical layerof an example MCPL. In some implementations, multiplexing andarbitration logic 1230 can also be provided as a layer separate from thelogical PHY 1110. In one example, the LPIF 1205 can be provided as theinterface on either side of this MuxArb layer 1230. The logical PHY 1110can interface with the physical PHY (e.g., the analog front end (AFE)1105 of the MCPL PHY) through another interface.

The LPIF can abstract the PHY (logical and electrical/analog) from theupper layers (e.g., 1210, 1215, 1220, 1225) such that a completelydifferent PHY can be implemented under LPIF transparent to the upperlayers. This can assist in promoting modularity and re-use in design, asthe upper layers can stay intact when the underlying signalingtechnology PHY is updated, among other examples. Further, the LPIF candefine a number of signals enabling multiplexing/demultiplexing, LSMmanagement, error detection and handling, and other functionality of thelogical PHY. For instance, Table 1 summarizes at least a portion ofsignals that can be defined for an example LPIF:

TABLE 1 Signal Name Description Rst Reset Lclk Link Clock-8UI of PHYclock Pl_trdy Physical Layer is ready to accept data, data is acceptedby Physical layer when Pl_trdy and Lp_valid are both asserted.Pl_data[N-1:0][7:0] Physical Layer-to-Link Layer data, where N equalsthe number of lanes. Pl_valid Physical Layer-to-Link Layer signalindicating data valid Pl_Stream[7:0] Physical Layer-to-Link Layer signalindicating the stream ID received with received data Pl_error Physicallayer detected an error (e.g., framing or training) Pl_AlignReq PhysicalLayer request to Link Layer to align packets at LPIF width boundaryPl_in_L0 Indicates that link state machine (LSM) is in L0 Pl_in_retrainIndicates that LSM is in Retrain/Recovery Pl_rejectL1 Indicates that thePHY layer has rejected entry into L1. Pl_in_L12 Indicates that LSM is inL1 or L2. Pl_LSM (3:0) Current LSM state information Lp_data[N-1:0][7:0]Link Layer-to-Physical Layer Data, where N equals number of lanes.Lp_Stream[7:0] Link Layer-to-Physical Layer signal indicating the streamID to use with data Lp_AlignAck Link Layer to Physical layer indicatesthat the packets are aligned LPIF width boundary Lp_valid LinkLayer-to-Physical Layer signal indicating data valid Lp_enterL1 LinkLayer Request to Physical Layer to enter L1 Lp_enterL2 Link LayerRequest to Physical Layer to enter L2 Lp_Retrain Link Layer Request toPhysical Layer to Retrain the PHY Lp_exitL12 Link Layer Request toPhysical Layer to exit L1, L2 Lp_Disable Link Layer Request to PhysicalLayer to disable PHY

As noted in Table 1, in some implementations, an alignment mechanism canbe provided through an AlignReq/AlignAck handshake. For example, whenthe physical layer enters recovery, some protocols may lose packetframing. Alignment of the packets can be corrected, for instance, toguarantee correct framing identification by the link layer.Additionally, as shown in FIG. 13 , the physical layer can assert aStallReq signal when it enters recovery, such that the link layerasserts a Stall signal when a new aligned packet is ready to betransferred. The physical layer logic can sample both Stall and Valid todetermine if the packet is aligned. For instance, the physical layer cancontinue to drive trdy to drain the link layer packets until Stall andValid are sampled asserted, among other potential implementations,including other alternative implementations using Valid to assist inpacket alignment.

Various fault tolerances can be defined for signals on the MCPL. Forinstance, fault tolerances can be defined for valid, stream, LSMsideband, low frequency side band, link layer packets, and other typesof signals. Fault tolerances for packets, messages, and other data sentover the dedicated data lanes of the MCPL can be based on the particularprotocol governing the data. In some implementations, error detectionand handling mechanisms can be provided, such as cyclic redundancy check(CRC), retry buffers, among other potential examples. As examples, forPCIe packets sent over the MCPL, 32-bit CRC can be utilized for PCIetransaction layer packets (TLPs) (with guaranteed delivery (e.g.,through a replay mechanism)) and 16-bit CRC can be utilized for PCIelink layer packets (which may be architected to be lossy (e.g., wherereplay is not applied)). Further, for PCIe framing tokens, a particularhamming distance (e.g., hamming distance of four (4)) can be defined forthe token identifier; parity and 4-bit CRC can also be utilized, amongother examples. For IDI packets, on the other hand, 16-bit CRC can beutilized.

In some implementations, fault tolerances can be defined for link layerpackets (LLPs) that include requiring a valid signal to transition fromlow to high (i.e., 0-to-1) (e.g., to assist in assuring bit and symbollock). Further, in one example, a particular number of consecutive,identical LLPs can be defined to be sent and responses can be expectedto each request, with the requestor retrying after a response timeout,among other defined characteristics that can be used as the basis ofdetermining faults in LLP data on the MCPL. In further examples, faulttolerance can be provided for a valid signal, for instance, throughextending the valid signal across an entire time period window, orsymbol (e.g., by keeping the valid signal high for eight UIs).Additionally, errors or faults in stream signals can be prevented bymaintaining a hamming distance for encodings values of the streamsignal, among other examples.

Implementations of a logical PHY can include error detection, errorreporting, and error handling logic. In some implementations, a logicalPHY of an example MCPL can include logic to detect PHY layer de-framingerrors (e.g., on the valid and stream lanes), sideband errors (e.g.,relating to LSM state transitions), errors in LLPs (e.g., that arecritical to LSM state transitions), among other examples. Some errordetection/resolution can be delegated to upper layer logic, such as PCIelogic adapted to detect PCIe-specific errors, among other examples.

In the case of de-framing errors, in some implementations, one or moremechanisms can be provided through error handling logic. De-framingerrors can be handled based on the protocol involved. For instance, insome implementations, link layers can be informed of the error totrigger a retry. De-framing can also cause a realignment of the logicalPHY de-framing. Further, re-centering of the logical PHY can beperformed and symbol/window lock can be reacquired, among othertechniques. Centering, in some examples, can include the PHY moving thereceiver clock phase to the optimal point to detect the incoming data.“Optimal,” in this context, can refer to where it has the most marginfor noise and clock jitter. Re-centering can include simplifiedcentering functions, for instance, performed when the PHY wakes up froma low power state, among other examples.

Other types of errors can involve other error handling techniques. Forinstance, errors detected in a sideband can be caught through a time-outmechanism of a corresponding state (e.g., of an LSM). The error can belogged and the link state machine can then be transitioned to Reset. TheLSM can remain in Reset until a restart command is received fromsoftware. In another example, LLP errors, such as a link control packeterror, can be handled with a time-out mechanism that can re-start theLLP sequence if an acknowledgement to the LLP sequence is not received.

FIGS. 14A-14C illustrate representations of example bit mappings on datalanes of an example MCPL for various types of data. For instance, anexample MCPL can include fifty data lanes. FIG. 14A illustrates a firstbit mapping of example 16 byte slots in a first protocol, such as IDI,that can be sent over the data lanes within an 8UI symbol, or window.For instance, within the defined 8UI window, three 16 byte slots,including a header slot, can be sent. Two bytes of data remain, in thisexample, and these remaining two bytes can be utilized CRC bits (e.g.,in lanes DATA[48] and DATA[49]).

In another example, FIG. 14B illustrates a second example bit mappingfor PCIe packet data sent over the fifty data lanes of an example MCPL.In the example of FIG. 14B, 16 bytes packets (e.g., transaction layer(TLP) or data link layer (DLLP) PCIe packets) can be sent over the MCPL.In an 8UI window, three packets can be sent, with the remaining twobytes of bandwidth left unused within the window. Framing tokens can beincluded in these symbols and used to locate the start and end of eachpacket. In one example of PCIe, the framing utilized in the example ofFIG. 14B can be the same as those token implemented for PCIe at 8 GT/s.

In yet another example, illustrated in FIG. 14C, an example bit mappingof link-to-link packets (e.g., LLP packets) sent over an example MCPL isshown. LLPs can be 4 bytes each and each LLP (e.g., LLP0, LLP1, LLP2,etc.) can be sent four consecutive times, in accordance with faulttolerance and error detection within an example implementation. Forinstance, failure to receive four consecutive identical LLPs canindicate an error. Additionally, as with other data types, failure toreceive a VALID in a proceeding time window, or symbol, can alsoindicate an error. In some instances, LLPs can have fixed slots.Additionally, in this example, unused, or “spare,” bits in the byte timeperiod, can result in logical 0s being transmitted over two of the fiftylanes (e.g., DATA[48-49]), among other examples.

Turning to FIG. 15 , a simplified link state machine transition diagram1400 is shown together with sideband handshaking utilized between thestate transitions. For instance, a Reset.Idle state (e.g., where phaselock loop (PLL) lock calibration is performed) can transition, through asideband handshake, to a Reset.Cal state (e.g., where the link isfurther calibrated). Reset.Cal can transition, through a sidebandhandshake, to a Reset.ClockDCC state (e.g., where duty cycle correction(DCC) and delay-locked looping (DLL) lock can be performed). Anadditional handshake can be performed to transition from Reset.ClockDCCto a Reset.Quiet state (e.g., to deassert the Valid signal). To assistin alignment of signaling on the lanes of the MCPL, the lanes can becentered through a Center.Pattern state.

In some implementations, as shown in the example of FIG. 16 , during theCenter.Pattern state, the transmitter can generate training patterns orother data. The receiver can condition its receiver circuitry to receivesuch training patterns, for instance, by setting the phase interpolatorposition and vref position and setting the comparator. The receiver cancontinuously compare the patterns received with expected patterns andstore the result in a register. After one set of patterns are complete,the receiver can increment the phase interpolator setting keeping thevref the same. The test pattern generation and comparison process cancontinue and new compare results can be stored in the register with theprocedure repeatedly stepping through all phase interpolator values andthrough all values of vref. The Center.Quiet state can be entered whenthe pattern generation and comparison process is all complete. Followingthe centering of the lanes through the Center.Pattern and Center Quietlink states, a sideband handshake (e.g., using an LSM sideband signalover the dedicated LSM sideband lane of the link) can be facilitated totransition to a Link. Init state to initialize the MCPL and enablesending of data on the MCPL.

Returning momentarily to the discussion of FIG. 15 , as noted above,sideband handshakes can be used to facilitate link state machinetransitions between dies or chips in a multi-chip package. For instance,signals on the LSM sideband lanes of an MCPL can be used to synchronizethe state machine transitions across the die. For example, when theconditions to exit a state (e.g., Reset.Idle) are met, the side that metthose conditions can assert, on its outbound LSM_SB lane, an LSMsideband signal and wait for the other remote die to reach the samecondition and assert an LSM sideband signal on its LSM_SB lane. Whenboth LSM_SB signals are asserted the link state machine of eachrespective die can transition to the next state (e.g., a Reset.Calstate). A minimum overlap time can be defined during which both LSM_SBsignals should be kept asserted prior to transitioning state. Further, aminimum quiesce time can be defined after LSM_SB is de-asserted to allowfor accurate turn-around detection. In some implementations, every linkstate machine transition can be conditioned on and facilitated by suchLSM_SB handshakes.

FIG. 17 is a more detailed link state machine diagram 1700, illustratingat least some of the additional link states and link state transitionsthat can be included in an example MCPL. Transitions between each of thelink states can be facilitated through sideband handshaking provided bya sideband lane of the MCPL. In some implementations, an example linkstate machine can include, among the other states and state transitionsillustrated in FIG. 17 , a “Directed Loopback” transition can beprovided to place the lanes of an MCPL into a digital loopback. Forinstance, the receiver lanes of an MCPL can be looped back to thetransmitter lanes after the clock recovery circuits. An “LB Recenter”state can also be provided in some instances, which can be used to alignthe data symbols. Additionally, as shown in FIG. 15 , MCPL can supportmultiple link states, including an active L0 state and low power states,such as an L1 idle state, and L2 sleep state, among potentially otherexamples.

FIG. 18 is a simplified block diagram 1800 illustrating an example flowin a transition between an active state (e.g., L0) and a low-power, oridle, state (e.g., L1). In this particular example, a first device 1805and a second device 1810 are communicatively coupled using an MCPL.While in the active state, data is transmitted over the lanes of theMCPL (e.g., DATA, VALID, STREAM, etc.). Link layer packets (LLPs) can becommunicated over the lanes (e.g., data lanes, with the stream signalindicating that the data is LLP data), to assist in facilitating linkstate transitions. For instance, LLPs can be sent between the first andsecond devices 1805, 1810 to negotiate entry from L0 into L1. Forinstance, upper layer protocols supported by the MCPL can communicatethat entry into L1 (or another state) is desired and the upper layerprotocols can cause LLPs to be sent over the MCPL to facilitate a linklayer handshake to cause the physical layer to enter L1. For instance,FIG. 18 shows at least a portion of LLPs sent including an “Enter L1”request LLP sent from the second (upstream) device 1810 to the first(downstream) device 1805. In some implementations, and upper levelprotocols, the downstream port does not initiate the entry into L1. Thereceiving first device 1805 can send a “Change to L1” request LLP inresponse, which the second device 1810 can acknowledge through a “Changeto L1” acknowledgement (ACK) LLP, among other examples. Upon detectingcompletion of the handshake, the logical PHY can cause a sideband signalto be asserted on a dedicated sideband link to acknowledge that the ACKwas received and that the device (e.g., 1805) is ready for and expectingentry into L1. For instance, the first device 1805 can assert a sidebandsignal 1815 sent to the second device 1810 to confirm receipt of thefinal ACK in the link layer handshake. Additionally, the second device1810 can also assert a sideband signal in response to sideband signal1815 to notify the first device 1805 of the first device's sideband ACK1805. With the link layer control and sideband handshakes completed, theMCPL PHY can be transitioned into the L1 state causing all lanes of theMCPL to be put into idle power savings mode, including respective MCPLstrobes of the 1820, 1825 of the devices 1805, 1810. The L1 can beexited upon upper level layer logic of one of the first and seconddevices 1805, 1810 requesting re-entry into L0, for instance, inresponse to detecting data to be sent to the other device over the MCPL.

As noted above, in some implementations, an MCPL can facilitatecommunication between two devices supporting potentially multipledifferent protocols, and the MCPL can facilitate communicationsaccording to potentially any one of the multiple protocols over thelanes of the MCPL. Facilitating multiple protocols, however, cancomplicate entry and reentry into at least some link states. Forinstance, while some traditional interconnects have a single upper layerprotocol assuming the role of master in state transitions, animplementation of MCPL with multiple different protocols effectivelyinvolves multiple masters. As an example, as shown in FIG. 18 , each ofPCIe and IDI can be supported between two devices 1805, 1810 over animplementation of an MCPL. For instance, placing the physical layer intoan idle or low power state may be conditioned on permission first beingobtained from each of the supported protocols (e.g., both PCIe and IDI).

In some instances, entry into L1 (or another state) may be requested byonly one of the multiple, supported protocols supported for animplementation of an MCPL. While there may be a likelihood that theother protocols will likewise request entry into the same state (e.g.,based on identifying similar conditions (e.g., little or no traffic) onthe MCPL), the logical PHY can wait until permission or instructions arereceived from each upper layer protocol before actually facilitating thestate transition. The logical PHY can track which upper layer protocolshave requested the state change (e.g., performed a correspondinghandshake) and trigger the state transition upon identifying that eachof the protocols have requested the particular state change, such as atransition from L0 to L1 or another transition that would affect orinterfere with other protocols' communications. In some implementations,protocols can be blind as to their at least partial dependence on otherprotocols in the system. Further, in some instances, a protocol mayexpect a response (e.g., from the PHY) to a request to enter aparticular state, such as a confirmation or rejection of the requestedstate transition. Accordingly, in such instances, while waiting forpermission from other supported protocols for entry into an idle linkstate, the logical PHY can generate synthetic responses to a request toenter the idle state to “trick” the requesting upper layer protocol intobelieving that a particular state has been entered (when, in reality,the lanes are still active, at least until the other protocols alsorequest entry into the idle state). Among other potential advantages,this can simplify coordinating entry into the low power state betweenmultiple protocols, among other examples.

As noted above, the high bandwidth, low latency, time-multiplexedmultiprotocol support provided by on-package MCPLs can be extended tooff-package interconnect implementations. MCPL can be used to replacemore traditional general-purpose interconnects, such as MIPI and PCIe,in at least some contexts. In some cases, off-package MCPLs canout-perform conventional external interconnects. For instance, MCPLs aremulti-protocol capable while exhibiting lower power, shorter entry/exitlatencies, and providing higher bandwidth per pin than many otherconventional interconnects. While some channel and form factorspecifications can be defined for MCPLs, on- and off-package MCPLs canbe utilized in a variety of applications, from handheld mobile computersto high performance server systems.

In some instances, extending an MCPL to an off-package link can includethe provisioning of additional circuitry and logic (beyond what could beused to implement an on-package MCPL) to address issues introduced bythe generally longer lengths of links interconnected devices not on thesame package or die. For instance, lengthening an MCPL for anoff-package connection can introduce increased vulnerability tocrosstalk, insertion loss (introducing inter-symbol interference),increased channel attenuation, and difficulty in realizingsynchronization of lane sampling not only across the set of data lanesof the MCPL, but also between data lanes and corresponding valid lanes,among other example issues.

In one example, a combination of techniques can be utilized to addresscrosstalk reduction of an off-package MCPL. In one example, a passivesolution can be employed for the physical MCPL lanes. For instance,stripline routing and other techniques can be used to improve thesignal-to-ground ratio for the MCPL to greater than 1:2. Suchimprovements can provide sufficient crosstalk reduction for long MCPLchannels. In some implementations, active solutions can be additionallyor alternatively provided to mitigate crosstalk effect. For instance,active crosstalk reduction can be provided by enhancing MCPL receiverlogic to include a high-pass filter and a summer to add a weightedderivative of an aggressor signal (e.g., the two or more) most-dominantaggressors (on other lanes)) to a victim signal (on the target lane).For instance, a the high-pass filter can be implemented as an RC filterwith values of resistance (R) and capacitance (C) selected so that thefilter pole frequency is higher than the signaling frequency. The summercan be implemented using a switched capacitor circuit or continuous timeamplifier, among other example implementations. Indeed, the summercircuitry can be merged into a receiver sense amplifier to minimizepower. The filter output can then be added to the signal of the victimlane through an extra branch in the sense amplified. Other crosstalkcancellation and mitigation techniques can be also (or instead) beutilized including Eigen-Mode signalingbased crosstalk cancellationtechniques and extended crosstalk stress testing during link trainingand initialization, among other examples.

Longer MCPLs lengths can also introduce increased channel loss.Equalization techniques can be implemented in such instances to mitigatechannel loss. For instance, a continuous time linear equalization (CTLE)can be added to the receiver. For instance, CTLE can be provided with apeak gain of 2, AC-to-DC peaking of 6-12 dB, and unity gain bandwidth of16 GHz for 8 Gb/s operation. Low power CTLE can be achieved, forinstance, through advanced complementary metal-oxide semiconductor(CMOS) equalization circuits, to enable less than 2 pJ/b total linkpower efficiency.

As noted above, synchronizing lanes of an MCPL can be important forensuring accurate operation and sampling of the MCPL. As the length ofthe MCPL increases however and extend off-package, it can be moredifficult to precisely match the length of lane traces. This cancomplicate per-bundle training of the link and corresponding channelmatching. Accordingly, per-lane skew and phase adjustment can beimplemented for at least some of the MCPLs implemented in a system, suchas those MCPLs of longer lengths or interconnecting off-package. In oneexample, a phase adjustment circuit can be provided (e.g., at anoff-package interface and/or MCPL-compliant off-package components) foreach lane to be programmed, controlled, or otherwise managed by systemmanagement software, such as BIOS. The phase adjuster, in one example,can be implemented as a weighted inverter that controls a set ofparallel N-type and P-type metal-oxide-semiconductor logic (NMOS andPMOS) with the independent enabling. Iteratively enabling differentcombinations of the NMOS/PMOS logic can be used to adjust the phase.Such solutions, in some implementations, can be used in lieu of a fullphase interpolator (PI) (e.g., which other MCPLs (e.g., on-packagelinks) may utilize for per-cluster phase adjustment). In such examples,system management software can drive and use a hardware phase sweep todetermine the proper phase adjustment for each lane. The left and righteye margin phase adjustment positioned can be determined for each lane,allowing software to determine the optimal shift per lane to realizesynchronization across the MCPL lanes. As noted above, phaseinterpolation can be carried out in MCPLs at a lane cluster level.Per-lane phase adjustment can be utilized in combination withper-cluster phase interpolation. For instance, phase interpolation canbe carried out, first, at the cluster level, before progressing to aper-lane phase adjustment to fine-tune skew within the cluster, amongother examples.

Off-package MCPL links are subject to stronger electrostatic dischargeevents. To address this, circuitry of off-package, MCPL-compliantdevices or off-package MCPL interfaces can be provided withcomparatively larger electrostatic discharge structures (ESD), amongother enhancements. In total, enhancements provided at the receive,transmitter, and/or channel of an MCPL can realize longer-distance,off-package MCPLs with comparative power, latency, crosstalk, and jittercharacteristics as defined or expected for short, on-package MCPLs.Indeed, in some implementations, an MCPL can have specification-definedcompliance requirements and characteristics to ensure properinteroperation between devices to be interconnected using an MCPL.Compliance tests can be defined to test and approve devices (e.g., fromdifferent manufacturers or providers) for use in MCPL links.

MCPL logic and circuitry supporting off-package interconnects, such asdescribed above, can implement MCPLs that operate within the namespecifications of on-package MCPLs. For instance, a 10 dB off-packagechannel can be accommodated while staying within a 2 pJ/bit powerenvelope and supporting quick entry/exit times (e.g., 8UI), as withon-package MCPLs. Additionally, the same sideband signaling and statemachine logic of on-package MCPLs can be re-used within off-packageMCPLs. The MCPL sideband can allow for side-channel communications withremote die while the main link is under training or in power managementmode.

FIGS. 19-20 are simplified block diagrams 1900, 2000 illustratingexamples of MCPL compliance testing, in accordance with at least someembodiments. In some cases, existing link training and testing states ofthe MCPL state machine can be utilized, such as loopback states andother states (such as illustrated in FIG. 17 ). For instance, in FIG. 19, a loopback link state can be used to test signals output by thetransmitter of a device. To conduct the transmitter compliance test, thedevice under test (DUT) can be forced into a loopback state of the MCPLstate machine. As with other link state transitions of an MCPL, adefined MCPL sideband lane can be utilized to transition the transmitterlogic to the loopback state (e.g., from a reset state). In one example,as only a single component (die) may be present in the test (i.e., theDUT), the sideband handshake can be obtained by connecting the outboundsideband lane of the DUT transmitter to the inbound sideband lane of thesame DUT (i.e., with the transmitter handshaking with itself to forceentry into the loopback (or other test) state). Further set-up of thedevice under test can be conducted within an initialization quiet(INIT.QUIET) state, where the DUT link state machine is blocked due tocompliance strap setting. The input for receiver lanes can be obtainedfrom loopback, or by tying off receiver, and receiver error checking canbe masked off.

Continuing with the example of FIG. 19 , for transmitter testing, theDUT can act as a loopback master within the forced loopback state. Testinstructions can cause a pattern generator 1905 to generate testpatterns to be sent by MCPL transmitter logic of the DUT 1910. Forinstance, test patterns can be loaded by the transmitter logic into abuffer 1915 (e.g., first-in first-out (FIFO) buffer), passed through aSerDes 1920, to the analog front end (AFE) 1925 of the MCPL transmitterfor transmission on lanes of an MCPL channel. The channel can include aninterposer 1930, which can be scoped (e.g., by scope 1935) to detect thesignals 1940 emerging from the transmitter port of the component todetermine whether the signals are as expected (based on the providedtest patterns) and the transmitter operates as would be expected by anMCPL-compliant component.

Similarly, receiver logic of an MCPL component can be tested forcompliance, such as shown in FIG. 20 . In this example, the DUT 1910 canagain be forced into a loopback state, with the DUT acting, in thereceiver compliance test, as loopback slave. A bit error rate tester(BERT) 2005, or other tester, can be connected to the receiver of theDUT. During the test, all lanes except the lane under test can be loopedback and receiver lane error checking can be masked off, including errorchecking for valid, strobe, and stream lanes. During the test, thetester 2005 provides a test signal 2008 which is to be received andlooped back by the DUT. The receiver AFE 2010 receives the test signal2008, and remaining receiver logic (e.g., SERDES 2015, FIFO 2020) andthe logical PHY 2025 process the received test pattern under loopback,with pattern generator 2030 then attempting to transmit the test signalas received. The looped-back signal can be inspected (e.g., through ascope at interposer 2035) to determine if the receiving logic of the DUToperates as expected. Additionally, the tester 2005 can introduce jitterand otherwise challenge the quality of the receiver logic though thetest signals it generates and send to the DUT within the loopbacktesting, to ensure quality and compliance of the receiver logic, amongother examples.

As noted above, an interposer (e.g., 1930, 2035) can be utilized tofacilitate observation of the performance of an off-package DUT or anMCPL interface used to connect to off-package devices, among otherexamples allowing accessibility to device pins. In one example, aninterposer board can be provided to allow access to both the transmit(Tx) and receiver (Rx) pins so that Tx output can be taken to anoscilloscope for further spec compliance analysis or Rx marginorbit-error-rate can be tested with a tester (e.g., a jitter bit errorrate tester (J-BERT)). For wider usage of off-package MCPL technology,standardized pin foot-prints can be defined, such as a ball grid array(BGA) that connects the package to the printed circuit board (PCB) or aninterposer, among other examples.

Off-package deployment of MCPLs can enable a variety of high speed, lowpower, and low latency interconnect applications. In one example, shownin FIG. 21 , MCPL can be implemented to enable bit-sliced designs wheremultiple dies of the same type can be combined on a board to form alarger system. As one example, two Ethernet switches (e.g., 2105, 2110)can be interconnected by an MCPL 2115 to effectively form a singleunified switch with twice the number of ports. The MCPL-based design, inthis example, can allow a smaller die to be used for each of theswitches to implement a higher radix switch without developing a newdedicated die or package design.

In another example, the “last inch” problem facing high speed SerDessystems can be, at least in part, addressed by utilizing an off-packageMCPL. For instance, as shown in the simplified block diagram 2200 ofFIG. 22 , the SerDes component 2205 corresponding to a device 2210(e.g., within a high performance computer (HPC) system) can be designedto be relocated from the device 2210 (e.g., on-package) to the board2215, such that the SerDes component 2205 is placed in close proximityto the high speed switch 2220 through which data to/from device 2210 isto be routed to other devices (e.g., processing nodes) within the HPCsystem. The device 2210 can include an MCPL interface to connect to itscorresponding SerDes 2205 over an MCPL 2225. Data sent over thelonger-distance MCPL can be at a lower data rate than data communicatedbetween the high speed SerDes 2205 and switch 2220. By moving the SerDes2205 closer to its link partner (e.g., switch 2220), the overall networkspeed can be substantially increased (e.g., doubled or more) by limitinghighest-speed data rates to the shortest segment of the overall linkbetween the device 2210 and switch 2205, thereby increasing thebisection bandwidth. Data communicated over the MCPL (i.e., the longersegment of the overall link, in this example), on the other hand, whilestill “high speed,” can be sent at speeds multiple times lower than thedata sent (over link 2230) between the SerDes 2205 and switch 2220.

In addition to the examples above, extending MCPLs off-package canrealize still additional benefits and example use cases. For instance,on-package links (including MCPLs) can be subject to constrained (orrelatively small) power and thermal budgets, as such budgets can bedefined for the package as a whole. As an example, an encapsulatedpackage can be constrained by its geometry and construction in itsability to shed heat and enable other benefits of more flexible designarchitectures. Indeed, an MCPL implemented off-package on a main die orcircuit board can have larger thermal and power budgets and enable moreflexibility in designing to such limits. As another example, extendingMCPLs off-package can enable innovation beyond a single package providerand enable flexibility for original equipment manufacturers (OEMs)and/or end-users to support different usages with different companiondies without having to design or validate a new package. Furtherinnovation can be provided by enabling MCPL interfaces, or “slots,” toallow a package to be extended by connecting off-package using one ormore MCPLs to other components, including third-party components. Suchinnovation can enable expansion of protocols and services provided toMCPL data, including rich coherency and I/O protocols implemented on thehigh speed and low power MCPL interconnect technology.

Turning to FIGS. 23A-23B, simplified block diagrams 2300 a-b are shownillustrating an implementation of a block of MCPL logic capable of beingflexibly partitioned to support two or more separate links. MCPL logic2305 can be implemented within a package as an interface to off-packagecomponent or in a non-package component that is to interconnect to otherdevices, among other examples. In this implementation, the MCPL logic2305 can include upper layer logic to support data of two or moredifferent interconnect protocols. For instance, MCPL logic 2305 caninclude upper layer logic 2308 a-b of PCIe and IDI (although, in otherexamples, different and larger combinations of upper layer logic can besupported or provided in connection with an MCPL). Arbitration andmultiplexor logic 2310 can be used to multiplex and arbitrate data ofthe multiple supported protocols. The logical PHY 2312 can prepare thedata and cause the physical PHY, or Physical Coding Sublayer (PCS), 2315to send the data (including corresponding strobe, stream, and validsignals) on the dedicated physical lanes of the MCPL. In this example,clusters of MCPL lanes can be defined and associated with respectivelogical analog front ends (AFEs) 2320 a-b. In this example, each logicalAFE 2320 a-b is provided with a blocks of lanes that includes 25 datalanes, at least one stream lane, and at least one valid lane, at leastone differential strobe, and at least one sideband lane for eachdirection (Rx and Tx) (e.g., at least 60 lanes for each block).

MCPL logic 2305 can be implemented to configurably support either afull-link or partitioned-link mode. In the full link mode, as shown inFIG. 23A, all of the logical AFEs 2320 a-b (and the associated lanes)are utilized in a single off-package MCPL 2325 that provides 50 datalanes in each direction to connect to a single remote die package 2330.The MCPL logic, while capable of being arbitrated and operating inparallel to support multiple MCPLs, when in full-link mode, is dedicatedsolely to supporting the single MCPL 2325. Turning to FIG. 23B, in otherimplementations, the same logic 2305 can be configured (e.g., throughthe setting of an associated register value or other mechanism) tooperate in a partitioned-link mode, as shown in the example of FIG. 23B.In partitioned-link mode, partitions in each of the sub-blocks (e.g.,2308 a, 2308 b, 2310, 2315) can be enforced with each partitionconfigured to support signaling on one of the logical AFEs (e.g., 2320 aor 2320 b). This can allow two separate off-package MCPLs 2325 a,b to beimplemented, concurrently, using the same MCPL logic block 2305, eachresulting MCPL 2325 a,b using a respective block of lanes to provide 25data lanes, in each direction, for a link connecting to a different,respective remote die package (e.g., 2335, 2340). Indeed, the two MCPLs2325 a,b can operate independently, for instance, on separate clocks(strobes). For instance, the two MCPLs 2325 a,b can be trainedindependently (in cooperation with corresponding MCPL logic on theirpartner component 2335, 2340), one can send or receive data of one type(e.g., PCIe) while the other sends or receives data of another supportedtype (e.g., IDI), the two MCPLs 2325 a,b can multiplexing between datatypes differently, transition from idle to active modes independently,among other examples.

While the example of FIG. 23B shows partitioning of a single MCPL logicblock 2305 being configured to be partitioned into two equal 25 lanepartitions (e.g., 2325 a,b), it should be appreciated that otherimplementations may provide more than two blocks of lanes and logicwhich can be partitioned into three or more partitions. Further, somealternative implementations may provide differently sized partitions.For instance, one available partition may support a 30 data lane AFE andanother partition a 20 data lane AFE, which, when in full-link mode,also provides a 50 lane AFR (and corresponding MCPLs), among otherexamples.

Note that the apparatus', methods', and systems described above may beimplemented in any electronic device or system as aforementioned. Asspecific illustrations, the figures below provide exemplary systems forutilizing the invention as described herein. As the systems below aredescribed in more detail, a number of different interconnects aredisclosed, described, and revisited from the discussion above. And as isreadily apparent, the advances described above may be applied to any ofthose interconnects, fabrics, or architectures.

Referring to FIG. 24 , block diagram of a system 2400 is shown inaccordance with at least some embodiments. As shown in FIG. 24 ,multiprocessor system 2400 can be implemented as a point-to-pointinterconnect system, and include a first processor 2470 and a secondprocessor 2480 coupled via a point-to-point interconnect 2450. Each ofprocessors 2470 and 2480 may be some version of a processor. In oneembodiment, 2452 and 2454 are part of a serial, point-to-point coherentinterconnect fabric, such as a high-performance architecture.

While shown with only two processors 2470, 2480, it is to be understoodthat the scope of the present invention is not so limited. In otherembodiments, one or more additional processors may be present in a givenprocessor.

Processors 2470 and 2480 are shown including integrated memorycontroller units 2472 and 2482, respectively. Processor 2470 alsoincludes as part of its bus controller units point-to-point (P-P)interfaces 2476 and 2478; similarly, second processor 2480 includes P-Pinterfaces 2486 and 2488. Processors 2470, 2480 may exchange informationvia a point-to-point (P-P) interface 2450 using P-P interface circuits2478, 2488. As shown in FIG. 24 , IMCs 2472 and 2482 couple theprocessors to respective memories, namely a memory 2432 and a memory2434, which may be portions of main memory locally attached to therespective processors.

Processors 2470, 2480 each exchange information with a chipset 2490 viaindividual P-P interfaces 2452, 2454 using point to point interfacecircuits 2476, 2494, 2486, 2498. Chipset 2490 also exchanges informationwith a high-performance graphics circuit 2438 via an interface circuit2492 along a high-performance graphics interconnect 2439.

A shared cache (not shown) may be included in either processor oroutside of both processors; yet connected with the processors via P-Pinterconnect, such that either or both processors' local cacheinformation may be stored in the shared cache if a processor is placedinto a low power mode.

Chipset 2490 may be coupled to a first bus 2416 via an interface 2496.In one embodiment, first bus 2416 may be a Peripheral ComponentInterconnect (PCI) bus, or a bus such as a PCI Express bus or anotherthird generation I/O interconnect bus, although the scope of the presentinvention is not so limited.

As shown in FIG. 24 , various I/O devices 2414 are coupled to first bus2416, along with a bus bridge 2418 which couples first bus 2416 to asecond bus 2420. In one embodiment, second bus 2420 includes a low pincount (LPC) bus. Various devices are coupled to second bus 2420including, for example, a keyboard and/or mouse 2422, communicationdevices 2427 and a storage unit 2428 such as a disk drive or other massstorage device which often includes instructions/code and data 2430, inone embodiment. Further, an audio I/O 2424 is shown coupled to secondbus 2420. Note that other architectures are possible, where the includedcomponents and interconnect architectures vary. For example, instead ofthe point-to-point architecture of FIG. 24 , a system may implement amulti-drop bus or other such architecture.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

A design may go through various stages, from creation to simulation tofabrication. Data representing a design may represent the design in anumber of manners. First, as is useful in simulations, the hardware maybe represented using a hardware description language or anotherfunctional description language. Additionally, a circuit level modelwith logic and/or transistor gates may be produced at some stages of thedesign process. Furthermore, most designs, at some stage, reach a levelof data representing the physical placement of various devices in thehardware model. In the case where conventional semiconductor fabricationtechniques are used, the data representing the hardware model may be thedata specifying the presence or absence of various features on differentmask layers for masks used to produce the integrated circuit. In anyrepresentation of the design, the data may be stored in any form of amachine readable medium. A memory or a magnetic or optical storage suchas a disc may be the machine readable medium to store informationtransmitted via optical or electrical wave modulated or otherwisegenerated to transmit such information. When an electrical carrier waveindicating or carrying the code or design is transmitted, to the extentthat copying, buffering, or re-transmission of the electrical signal isperformed, a new copy is made. Thus, a communication provider or anetwork provider may store on a tangible, machine-readable medium, atleast temporarily, an article, such as information encoded into acarrier wave, embodying techniques of embodiments of the presentinvention.

A module as used herein refers to any combination of hardware, software,and/or firmware. As an example, a module includes hardware, such as amicro-controller, associated with a non-transitory medium to store codeadapted to be executed by the micro-controller. Therefore, reference toa module, in one embodiment, refers to the hardware, which isspecifically configured to recognize and/or execute the code to be heldon a non-transitory medium. Furthermore, in another embodiment, use of amodule refers to the non-transitory medium including the code, which isspecifically adapted to be executed by the microcontroller to performpredetermined operations. And as can be inferred, in yet anotherembodiment, the term module (in this example) may refer to thecombination of the microcontroller and the non-transitory medium. Oftenmodule boundaries that are illustrated as separate commonly vary andpotentially overlap. For example, a first and a second module may sharehardware, software, firmware, or a combination thereof, whilepotentially retaining some independent hardware, software, or firmware.In one embodiment, use of the term logic includes hardware, such astransistors, registers, or other hardware, such as programmable logicdevices.

Use of the phrase ‘configured to,’ in one embodiment, refers toarranging, putting together, manufacturing, offering to sell, importingand/or designing an apparatus, hardware, logic, or element to perform adesignated or determined task. In this example, an apparatus or elementthereof that is not operating is still ‘configured to’ perform adesignated task if it is designed, coupled, and/or interconnected toperform said designated task. As a purely illustrative example, a logicgate may provide a 0 or a 1 during operation. But a logic gate‘configured to’ provide an enable signal to a clock does not includeevery potential logic gate that may provide a 1 or 0. Instead, the logicgate is one coupled in some manner that during operation the 1 or 0output is to enable the clock. Note once again that use of the term‘configured to’ does not require operation, but instead focus on thelatent state of an apparatus, hardware, and/or element, where in thelatent state the apparatus, hardware, and/or element is designed toperform a particular task when the apparatus, hardware, and/or elementis operating.

Furthermore, use of the phrases ‘to,’ ‘capable of/to,’ and or ‘operableto,’ in one embodiment, refers to some apparatus, logic, hardware,and/or element designed in such a way to enable use of the apparatus,logic, hardware, and/or element in a specified manner. Note as abovethat use of to, capable to, or operable to, in one embodiment, refers tothe latent state of an apparatus, logic, hardware, and/or element, wherethe apparatus, logic, hardware, and/or element is not operating but isdesigned in such a manner to enable use of an apparatus in a specifiedmanner.

A value, as used herein, includes any known representation of a number,a state, a logical state, or a binary logical state. Often, the use oflogic levels, logic values, or logical values is also referred to as 1'sand 0's, which simply represents binary logic states. For example, a 1refers to a high logic level and 0 refers to a low logic level. In oneembodiment, a storage cell, such as a transistor or flash cell, may becapable of holding a single logical value or multiple logical values.However, other representations of values in computer systems have beenused. For example the decimal number ten may also be represented as abinary value of 1010 and a hexadecimal letter A. Therefore, a valueincludes any representation of information capable of being held in acomputer system.

Moreover, states may be represented by values or portions of values. Asan example, a first value, such as a logical one, may represent adefault or initial state, while a second value, such as a logical zero,may represent a non-default state. In addition, the terms reset and set,in one embodiment, refer to a default and an updated value or state,respectively. For example, a default value potentially includes a highlogical value, i.e. reset, while an updated value potentially includes alow logical value, i.e. set. Note that any combination of values may beutilized to represent any number of states.

The embodiments of methods, hardware, software, firmware or code setforth above may be implemented via instructions or code stored on amachine-accessible, machine readable, computer accessible, or computerreadable medium which are executable by a processing element. Anon-transitory machine-accessible/readable medium includes any mechanismthat provides (i.e., stores and/or transmits) information in a formreadable by a machine, such as a computer or electronic system. Forexample, a non-transitory machine-accessible medium includesrandom-access memory (RAM), such as static RAM (SRAM) or dynamic RAM(DRAM); ROM; magnetic or optical storage medium; flash memory devices;electrical storage devices; optical storage devices; acoustical storagedevices; other form of storage devices for holding information receivedfrom transitory (propagated) signals (e.g., carrier waves, infraredsignals, digital signals); etc., which are to be distinguished from thenon-transitory mediums that may receive information there from.

Instructions used to program logic to perform embodiments of theinvention may be stored within a memory in the system, such as DRAM,cache, flash memory, or other storage. Furthermore, the instructions canbe distributed via a network or by way of other computer readable media.Thus a machine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer), but is not limited to, floppy diskettes, optical disks,Compact Disc, Read-Only Memory (CD-ROMs), and magneto-optical disks,Read-Only Memory (ROMs), Random Access Memory (RAM), ErasableProgrammable Read-Only Memory (EPROM), Electrically ErasableProgrammable Read-Only Memory (EEPROM), magnetic or optical cards, flashmemory, or a tangible, machine-readable storage used in the transmissionof information over the Internet via electrical, optical, acoustical orother forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.). Accordingly, the computer-readablemedium includes any type of tangible machine-readable medium suitablefor storing or transmitting electronic instructions or information in aform readable by a machine (e.g., a computer).

The following examples pertain to embodiments in accordance with thisSpecification. One or more embodiments may provide an apparatus, asystem, a machine readable storage, a machine readable medium, and amethod to provide an interconnect interface to enable communication withan off-package device over a link including a plurality of lanes. Logicof the interconnect interface can include receiver logic (implemented atleast in part through hardware circuitry) to receive a valid signal fromthe off-package device on a dedicated valid lane of the link indicatingthat data is to arrive on a plurality of dedicated data lanes in theplurality of lanes, receive the data on the data lanes from theoff-package device sampled based on arrival of the valid signal, andreceive a stream signal from the off-package device on a dedicatedstream lane in the plurality of lanes, the stream signal correspondingto the data and indicates a particular data type of the data. Theparticular data type can be one of a plurality of different data typescapable of being received on the plurality of data lanes on the link.

In one example, the receiver logic is to determine a start of the databased on a start and duration of the valid signal.

In one example, the data is defined to be received following a number ofunit intervals of the valid signal.

In one example, the stream signal is received concurrently with data tocorrespond to the data.

In one example, the interconnect interface further includes statemachine logic to transition between a plurality of link states based onsideband signals received from the off-package device over a sidebandlane in the plurality of lanes.

In one example, the state machine logic is further to cause handshakesignals to be sent to the off-package device to facilitate thetransitions between the plurality of link states.

In one example, each of the valid signal, the data, and the streamsignal are sent in a respective one of a series of defined signalingwindows for the link, and each of the defined signaling windows is ofequal duration.

In one example, the valid signal is sent in a first one of the series ofsignaling windows, and the data and stream signal are to be sent in asecond one of the series of signaling windows immediately succeeding thefirst signaling window.

In one example, the data includes first data and the stream signalincludes a first stream signal. The receiver logic can be furtherconfigured to receive second data over at least a portion of theplurality of data lanes in a third one of the series of signalingwindows immediately succeeding the second signaling window, the seconddata being another one of the plurality of data types, and receive asecond stream signal over the stream lane in the third signaling window,the second stream signal indicating the other data type. The validsignal is to remain asserted through at least the second signalingwindow to indicate the first and second data.

In one example, two on-package components are provided that areconnected using an on-package link including another plurality of datalanes, an instance of the valid lane, and an instance of the streamlane, and the receiver logic is based on receiver logic for theon-package link.

In one example, the receiver logic is further to train the plurality oflanes to synchronize sampling phase for each lane, where phase controlis performed on a per-lane basis for the plurality of lanes.

In one example, each of the plurality of data types correspond to arespective one of a plurality of different protocols.

In one example, upper layer protocol logic of each of the plurality ofdifferent protocols, where the stream signal is used to invoke upperlayer protocol logic corresponding to the data type indicated in thestream signal.

In one example, data appearing on the data lanes is to be ignored withina particular signaling window immediately following a preceding windowin which the valid signal is not asserted.

One or more embodiments may provide an apparatus, a system, a machinereadable storage, a machine readable medium, and a method to provide aninterconnect interface to enable communication with an off-packagedevice over a link including a plurality of lanes, the interconnectinterface including transmitter logic (implemented at least in partthrough hardware circuitry) to send a valid signal to the off-packagedevice on a dedicated valid lane of the link indicating to theoff-package device that data is to be sent to the off-package device ona plurality of dedicated data lanes in the plurality of lanes, send thedata on the data lanes to the off-package device, and send a streamsignal to the off-package device on a dedicated stream lane in theplurality of lanes. The stream signal can correspond to the data andindicate a particular data type of the data, and the particular datatype can be one of a plurality of different data types capable of beingcommunicated on the plurality of data lanes on the link.

In one example, the plurality of lanes includes a second plurality ofdata lanes, a second valid lane, and a second stream lane, the secondplurality of data lanes, the second valid lane, and the second streamlane are coupled to another off-package device, and the receiver logicis partitioned and includes arbitration logic to concurrently senddifferent data streams to the particular off-package device and theother off-package device using the plurality of lanes.

In one example, each of the plurality of data types correspond to arespective one of a plurality of different protocols and the transmitterlogic includes upper layer protocol logic of each of the plurality ofdifferent protocols.

In one example, state machine logic is provided to transition between aplurality of link states based on sideband signals communicated with theoff-package device over a sideband lane in the plurality of lanes.

One or more embodiments may provide a system including a first device, asecond device remote from the first device, and a link connecting thefirst device to the second device. The link can include a plurality oflanes and the plurality of lanes can include a plurality of data lanes,a valid lane, and a stream lane. Data is to be sent from the firstdevice to the second device using the plurality of data lanes, thestream lane is to be used to send a stream signal to indicate a type ofthe data from a plurality of types, and the valid lane is to be used tosend a valid signal to indicate that the data is to be sent in animmediately subsequent signaling window.

In one example, the first device includes a processor and the seconddevice includes a serializer/deserializer (SerDes), the link includes afirst link, the system further includes a high speed switch coupled tothe SerDes by a second link, and the second link is shorter than thefirst link.

In one example, the second device includes continuous time linearequalization circuitry.

In one example, the link utilizes stripline routing through a circuitboard.

In one example, the system includes the circuit board.

In one example, the link further includes a sideband lane to be used tosend sideband handshake signals to facilitate link state transitions forthe link.

In one example, the link includes a first link and the first deviceincludes at least two components interconnected by a second link, thesecond link including a respective plurality of data lanes, a respectivevalid lane, and a respective stream lane.

In one example, the first link and second link both operate within acommon channel attenuation and power envelope.

In one example, the first link is at least three times longer than thesecond link.

In one example, the plurality of data lanes include a first plurality ofdata lanes, the valid lane includes a first valid lane, and the streamlane includes a first stream lane, the plurality of lanes includes asecond plurality of data lanes, a second valid lane, and a second streamlane, the first device includes transmitter logic to transmit data usingthe plurality of lanes, and the transmitter logic is partitionable.

In one example, the transmitter logic, when partitioned, supportscoupling to two or more devices, including the second device, using theplurality of lanes, where the second plurality of data lanes, the secondvalid lane, and the second stream lane are used to connect the firstdevice to a third device.

In one example, the transmitter logic, when is a full link mode, isunpartitioned, and the link includes the first and second pluralities ofdata lanes, the first and second valid lanes, and the first and secondstream lanes.

In one example, the system further includes a system manager,implemented at least in part in software, to assist in adjusting phaseof each of the lanes in the plurality of lanes such that sampling of theplurality of lanes is synchronized.

In one example, the first device includes a first switch and the seconddevice includes second switch and interconnecting the first and secondswitches with the link implements a high radix switch.

In one example, each of the first and second switch are Ethernetswitches.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary embodiments. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense. Furthermore, the foregoing use of embodiment andother exemplarily language does not necessarily refer to the sameembodiment or the same example, but may refer to different and distinctembodiments, as well as potentially the same embodiment.

1-22. (canceled) 23-42. (canceled)
 43. An apparatus comprising: a first die comprising: a port to couple to the first die to a second die over an interconnect, wherein the port comprises: protocol circuitry to generate first data based on a first protocol and second data based on a different second protocol; and physical layer circuitry to implement a physical layer of the interconnect, wherein the first data and the second data are to be sent on the physical layer from the first die to the second die, wherein the physical layer comprises a group of lanes comprising: a valid lane; a clock lane; a plurality of data lanes; and a sideband lane.
 44. The apparatus of claim 43, wherein the first die and the second die are on a same package.
 45. The apparatus of claim 43, wherein the first die and the second die are different packages.
 46. The apparatus of claim 43, wherein the first data and second data are to be time-multiplexed over the interconnect.
 47. The apparatus of claim 43, wherein the first protocol comprises a non-coherent protocol and the second protocol comprises a coherent protocol.
 48. The apparatus of claim 47, wherein the first protocol comprises a Peripheral Component Interconnect Express (PCIe)-based protocol.
 49. The apparatus of claim 43, wherein the clock lane is to implement a forward clock.
 50. The apparatus of claim 43, wherein mainband data is to be carried on the plurality of data lanes.
 51. The apparatus of claim 43, wherein the sideband lane is to carry sideband signals to coordinate link training of the interconnect.
 52. The apparatus of claim 51, wherein the sideband signals are to coordinate state transitions in the link training.
 53. The apparatus of claim 43, wherein the valid lane is to carry a valid signal to indicate data on the plurality of data lanes.
 54. The apparatus of claim 53, wherein a start of the valid lane corresponds to a start of the data on the plurality of data lanes.
 55. A method comprising: sending sideband data on a set of sideband lanes of an interconnect, wherein the interconnect couples a first die to a second die, the interconnect comprises a physical layer, and the physical layer comprises the sideband lanes, a valid lane, a plurality of data lanes, and a clock lane; configuring the interconnect based on information communicated on the set of sideband lanes; identifying data of a first one of a plurality of protocols; generating a valid signal to send on the valid lane to indicate the data; sending the data from the first die to the second die on the plurality of data lanes; sending a clock signal on the clock lane.
 56. The method of claim 55, further comprising: identifying second data of a second protocol in the plurality of protocols; generating a second valid signal to send on the valid lane to indicate the second data; sending the second data from the first die to the second die on the plurality of data lanes.
 57. A system comprising: a first die; a second die coupled to the first die by a die-to-die (D2D) link, wherein the second die comprises: a port to connect the second die to the D2D link, wherein the port comprises: first protocol circuitry to generate first data based on a first protocol; second protocol circuitry to generate second data based on a different second protocol; and physical layer circuitry to implement a physical layer of the link, wherein the first data and the second data are to be sent on the physical layer from the first die to the second die, wherein the physical layer comprises a group of lanes comprising: a valid lane; a clock lane; a plurality of data lanes; and a set of sideband lanes.
 58. The system of claim 57, wherein the first device comprises a processor.
 59. The system of claim 57, wherein one of the first device or the second device comprises an accelerator device.
 60. The system of claim 57, further comprising a package, wherein the package comprises the first and second dies.
 61. The system of claim 60, wherein the package comprises a system on chip (SoC).
 62. The system of claim 57, wherein: the clock lane is to implement a forward clock; mainband data is to be carried on the plurality of data lanes; the sideband lane is to carry sideband signals to coordinate link training of the link; and the valid lane is to carry a valid signal to indicate data on the plurality of data lanes. 